diff --git a/src/lib.zig b/src/lib.zig
index 60046b2b86852257db43bdd1550535156f9f2633..6f217856fa283a3f1900fbc6a1749021d9cd33dc 100644
--- a/src/lib.zig
+++ b/src/lib.zig
@@ -451,7 +451,7 @@ pub fn safeAdd(a: anytype, b: anytype) @TypeOf(a) {
     if (b >= 0) {
         return a + @as(@TypeOf(a), @intCast(b));
     }
-    return a - @as(@TypeOf(a), @intCast(-b));
+    return a - @as(@TypeOf(a), @intCast(-@as(OneBiggerInt(@TypeOf(b)), b)));
 }
 
 pub fn readBytesAlloc(reader: anytype, alloc: std.mem.Allocator, len: usize) ![]u8 {
@@ -651,3 +651,9 @@ pub fn joinPartial(comptime P: type, a: P, b: P) P {
     }
     return temp;
 }
+
+pub fn OneBiggerInt(comptime T: type) type {
+    var info = @typeInfo(T);
+    info.Int.bits += 1;
+    return @Type(info);
+}